We have introduced neutron and electron irradiation defects in bulk YBCO melt-textured materials. The defects and their effect on the critical current density (Jc) have been examined. The enhancement of Jc is found to be heavily dependent on the type and energy of the beam as well as on the direction of the beam with respect to the crystal. Two types of defects have been identified in neutron irradiated YBCO by positron annihilation experiments. The large defects (∼ 20 Å) correlate with the enhancement of Jc and are 103 times more effective in flux pinning than point defects.
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